1. Field of the Invention
The invention involves a photographic, silver halide, recording material for making black and white negative images having ultrahigh contrast and a process for making a black and white negative image by using such a material.
2. Description of the Related Art
In photomechanical reproduction, continuous tone images must frequently be converted into halftone images. Used for this purpose are silver halide materials that are developed by special processes to ultrahigh contrast, that is, to a maximum slope of the density curve of more than 10. Known examples are litho-graphic processes with sulfite-poor hydroquinone developers containing formaldehyde. Development in the presence of hydrazine compounds has been especially important recently.
In these processes, certain amino compounds are frequently used to increase contrast. Thus, EP-00 32 456-B1 claims a process in which a recording material is processed in the presence of a hydrazine compound with a hydroquinone-3-pyrazolidinone developer containing a contrast-enhancing quantity of an amino compound.
Developers containing a contrast-enhancing quantity of an amino compound have disadvantages. The required concentration of the amino compound is considerable and often approaches the limits of solubility. If temperature increase or concentration changes slightly due to water dilution during use, the solubility limits can be easily exceeded and the amino compound precipitates. This can lead to irregular development and to contamination of the recording material and the developing machines. Because of their volatility, the precipitated amino compounds can also reach remote parts of the developing machines, causing contamination and corrosion.
The use of developers containing amino compounds is also accompanied by a very unpleasant odor, due to the required high concentration and the volatility of these compounds.
Because the amino compounds have a limited solubility, it is difficult to formulate the conventional developer concentrates for commercial use. EP-A-02 03 521 does indeed disclose the use of salts of certain sulfonic or carboxylic acids as solubilizers. However, the other cited problems are not affected by such additives.
The known developers usually have a pH above 11. Therefore, they are not adequately stable in use and highly corrosive to parts of developing machines. German OS DE-A-43 10 327 describes a process for making negative images having ultrahigh contrast. In this process, the silver halide recording material is developed in the presence of compounds having at least one quaternary nitrogen atom and at least one tertiary amine function in the molecule.
EP-04 73 342-A1 describes a photographic silver halide material that can be developed to ultrahigh contrast in a developer having a pH&lt;11. The photosensitive coating of this material contains a hydrazine compound of a certain formula and an amino or quaternary onium compound and is adjusted to a pH of at least 5.9.
U.S. Pat. No. 4,975,354 discloses incorporating in the silver halide materials, in addition to hydrazine compounds, certain secondary or tertiary amino compounds, also containing at least three oxyethylene units in their molecule as contrast boosters.
EP 04 22 677 describes the use of tertiary amino compounds having at least three oxyethylene units in the molecule as development accelerators in developer solutions, that also act in the presence of hydrazine compounds.
EP 05 39 998 claims silver halide materials containing, in addition to hydrazine compounds, thioether compounds having tertiary amino groups.
These contrast-enhancing additives can yield satisfactory images only when used in relatively large quantities. This has adverse effects on the properties of the recording material, for example, storage stability, wet pressure sensitivity, and drying behavior.